[sdiy] Theremin controller

[Grant Richter]

I have made a fairly useful proximity controller for the Synthi A.

The design is based on the "Two Chip Theremin" in Practical  
Electronics magazine from the 70s.

It uses three CD4046 chips. One chip acts as a square wave reference  
frequency between 150 to 350 kHz. Use polystyrene or polyester caps  
for the timing caps.

The second 4046 acts like a tunable oscillator, and you solder the  
theremin antenna right to one of the pins with the timing cap on it.  
Use 40 to 60 milliHenry inductor (two or three 20 milliHenry  
inductors in series, 20 milliHenry is the largest inductor Mouser  
sold at the time)  in series with the antenna to act as a matching  
network and get a 24-36 inch sensing distance. With out the inductor  
you will only have about a 6 inch sensing distance.

The EXOR gate in the second 4046 acts as a mixer and extracts the  
lower sideband difference frequency. A simple passive RC filter  
attenuates the upper sideband so you don't confuse the frequency to  
voltage convertor.

A third CD4046 set up as PLL converts the varying frequency into a  
voltage.

CD4046s are about 29 cents apiece, so the main circuitry parts cost  
is around 2 dollars. Using the antenna matching inductors makes it  
more expensive.

If people are interested I could write up the project for  
musicsynthesizer.com

On Mar 10, 2007, at 11:55 AM, John Luciani wrote:

> On 3/10/07, James Dunn <james at 4thharmonic.com> wrote:
>> Can someone point me to a simple Theremin controller schematic on the
>> web somewhere? I can't seem to find anything very useful - I just  
>> want a
>> CV out based on proximity of hand, etc. The PAIA Theremax looks  
>> like a
>> lot of parts, but more importantly the miniature transformers aren't
>> labelled with any value - does anyone know what they might be?
>>
>> James
>>
>
> Checkout the Feb 96 Electronic Musician article "Build the EM  
> Theremnin"
> written by Bob Moog. There is a copy of the  schematic at the Moog  
> Music
> website ---
>> http://www.moogmusic.com/manuals/HotRodEtherwav.pdf
>
>
>
> A couple of the circuits that I have seen have 100uH inductors and
> oscillate around
> 300KHz.
>
> (* jcl *)
>
> -- 
> http://www.luciani.org